153. As of April 17, 2011, there were 153 dead dolphins and whales that the National Oceanic and Atmospheric Administration (NOAA) recovered from Gulf of Mexico shores following the BP oil spill. But a study published in the journal Conservation Letters reveals that this number reflects only a fraction of the dolphins and whales killed by the catastrophe. “The Deepwater oil spill was the largest in U.S. history, however, the recorded impact on wildlife was relatively low,” says lead author Rob Williams, Ph.D., a member of the Marine Mammal Research Unit at the University of British Columbia. “Reports have implied that the number of carcasses recovered equals the number of animals killed by the spill.”

The study looked at the annual death rates of dolphins, whales and porpoises over the past decade. Of the estimated 4,474 that died each year, just 17 carcasses washed up on shore. From this data, the researchers determined that the carcasses found after the BP spill accounted for only 2% of the dolphins and whales that actually died. “Carcass counts are hugely misleading if used to measure the disaster’s death toll,” says co-author Scott Kraus, Ph.D., vice president of research at the New England Aquarium. “The animals that come up on the beach are animals that happen to float after death. They also happen to be carried by currents or winds toward shore. So the occurrence of a whale or a dolphin on a beach is serendipitous in many ways.”

This past year featured many “unusual mortality events,” according to NOAA. Many dead dolphins that washed ashore were newly born or stillborn calves, some barely three feet in length. Since dolphins are pregnant for 12 months, scientists are speculating that oil and dispersants inhaled by the vulnerable mammals during last year’s spill may now be causing miscarriages.

Blubber samples have been sent to labs to determine the exact cause of deaths, but the U.S. government is slow to reveal their findings due to an ongoing civil and criminal case against BP. “The public’s right to know is important. But the public’s right to collect damages from the responsible party is equally important,” says Ben Sherman, a public relations officer at NOAA. Independent scientists have faced several legal obstacles in their attempts to conduct and allocate research throughout the BP catastrophe. Kraus noted that data is off because there is no “baseline” for scientists to pull from. “The biological and ecological effects will not be known for many years, if ever,” he says.

Increased funding for deep sea biology research is needed to create that baseline for scientists to fully analyze the impacts of oil and chemical spills or radiation leaks. Kraus adds that the companies that extract the resources should cover those costs.